The present invention is related to biaxially textured metallic substrates and articles made therefrom, and more particularly to methods of forming substrates and articles having a biaxial texture.
Since the discovery of superconducting materials having critical temperatures that exceed the temperature of liquid nitrogen, there has been a concerted effort to utilize these materials for various applications, such as in wires and electronic devices. In order to be commercially viable, these applications require high temperature superconducting materials with a high critical current density. Critical current density, Jc, is the maximum current density a superconductor can carry at a given temperature and magnetic field. One such high temperature superconducting (HTS) material is a composite oxide of RE, Ba and Cu, (ReBCO) and in particular, REBa2Cu3Ox (wherein RE represents at least one of the following rare earth elements: Y, La, Sm, Nd, Eu, Gd, Dy, Ho, Er, Tm, Yb, or Lu).
Current materials research aimed at fabricating high temperature superconducting ceramics in conductor configurations for bulk, practical applications, is largely focused on powder-in-tube methods. Such methods have proven quite successful for the Bixe2x80x94(Pb)xe2x80x94Srxe2x80x94Caxe2x80x94Cuxe2x80x94O (BSCCO) family of superconductors due to their unique mica-like mechanical deformation characteristics. In high magnetic fields, however, this family of superconductors is generally limited to applications below 30xc2x0 K. In the ReBCO Tlxe2x80x94(Pb, Bi)xe2x80x94Srxe2x80x94(Ba)xe2x80x94Caxe2x80x94Cuxe2x80x94O and Hgxe2x80x94(Pb)xe2x80x94Srxe2x80x94(Ba)xe2x80x94Caxe2x80x94Cuxe2x80x94O families of superconductors, some of the compounds have much higher intrinsic limits and can be used at higher temperatures.
It has been demonstrated that these superconductors possess a high Jc at high temperatures when fabricated as single crystals or in essentially single-crystal form as epitaxial films on single crystal substrates such as SrTiO3 and LaAlO3. An epitaxial film is one whose crystalline lattice is nearly perfectly aligned with the lattice of the substrate on which it is deposited. These superconductors have so far been intractable to conventional ceramics and materials processing techniques to form long lengths of a polycrystalline conductor with a Jc comparable to epitaxial films. This is primarily because the poor electrical connections at the boundaries between crystalline grains, which is known in the art as the xe2x80x9cweak-linkxe2x80x9d effect.
Thin-film materials having perovskite-like structures are important in superconductivity, ferroelectrics, and electro-optics. Many applications using these materials require, or would be significantly improved by single crystal, c-axis oriented perovskite-like films grown on single-crystal or highly aligned metal or metal-coated substrates. For instance, Yxe2x80x94Ba2xe2x80x94Cu3xe2x80x94O (YBCO) is an important superconducting material for the development of superconducting current leads, transmission lines, motor and magnetic windings, and other electrical conductor applications. When cooled below their transition temperature, Tc, superconducting materials have no electrical resistance and carry electrical current without energy dissipation.
One technique for fabricating a superconducting wire or tape is to deposit a YBCO film on a metallic substrate. Superconducting YBCO has been deposited on polycrystalline metals in which the YBCO is c-axis oriented, but not aligned in-plane. To carry high electrical currents, however, the YBCO films must be biaxially textured, preferably c-axis oriented, with effectively no large-angle grain boundaries, since such grain boundaries are detrimental to the current-carrying capability of the material. YBCO films deposited on polycrystalline metal substrates do not generally meet this criterion.
Many electronic, magnetic, or superconductor device applications require control of the grain boundary character of the device materials. For example, grain boundary character is very important in high temperature superconductors. It is known that the critical current density through a grain boundary may be reduced significantly for misorientation angles greater than 5xc2x0-10xc2x0. It is thus desirable to obtain superconducting deposits in which the number of grain boundaries with misorientation angles greater than 5xc2x0-10xc2x0 is minimized. For conductors in which the superconducting deposit is epitaxial with an underlying metallic or oxide buffer layer or substrate, it is desirable to minimize the number of grain boundaries with misorientations greater than 5xc2x0-10xc2x0. This is accomplished if the texture of the substrate has grain orientations which vary by no more than 5xc2x0-10xc2x0. Useful superconducting layers may be obtained using substrates with a larger spread in grain orientation. However, the properties of the superconductor deposit are expected to improve with a biaxially textured substrate having a narrow spread in grain orientation.
The effects of grain boundary characteristics on current transmission have been clearly demonstrated for certain materials, for example, the material known as YBCO. See Dimos, et al. (1988) Phys. Rev. Lett. 61:219; and Dimos, et al. (1990) Phys. Rev. Lett. 41:4038. For clean, stoichiometric boundaries, the grain boundary critical current (Jc(gb)) appears to be determined primarily by grain boundary misorientation. The dependence of Jc(gb) on misorientation angles for YBCO has been determined by Dimos et al., supra, for grain boundary types which can be formed in epitaxial films on bicrystal substrates. These include [001] tilt, [100] tilt, and [100] twist boundaries. In each case, however, high angle boundaries were found to be weak-linked.
Recently, the Dimos work has been extended to artificially fabricated [001] tilt bicrystals in Tl2Ba2CaCu2O8 (A. H. Cardona, et al., Appl. Phys. Lett., 62 (4), 411, 1993)), Ndl0.85Ce0.15CuO4, Tl2Ba2Ca2Cu3Ox(M. Kawasaki, et al., Appl. Phys. Lett., 62 (4), 417 (1993)), and TlBa2Ca2Cu2Ox(T. Nabatame, et al., Appl. Phys. Lett. 65 (6), 776 (1994)). In each of these cases, it was found that, as in the case of YBCO, Jc depends strongly on grain boundary misorientation angle. Although no measurements have been made on the material known as Bi-2223, data on current transmission across artificially fabricated grain boundaries in the material termed Bi-2212 indicate that most large angle [001] tilt (M. Kawasaki, et al., Appl. Phys. Lett., 62 (4), 417 (1993)) and twist boundaries are weak links, with the exception of some coincident site lattice (CSL) related boundaries (N. Tomita, et al., Jpn. J. Appl. Phys., 29 (1990) L30; N. Tomita, et al., Jpn. J. Appl. Phys., 31, L942 (1992), J. L. Wang, et al., Physica C, 230, 189 (1994)). It is likely that the variation in Jc with [001] tilt grain boundary misorientation in materials Bi-2212 and Bi-2223 is similar to that observed in the well characterized cases of YBCO and TI-based superconductors.
Hence, in order to fabricate high temperature superconductors with a high Jc, it is necessary to have a good biaxial texture. This has been shown to result in significant improvement in the superconducting properties of YBCO films. Y. Iijima, et al., Appl. Phys., 74, 1905 (1993); R. P. Reade et. al., Appl. Phys. Lett., 61, 2231 (1992); X. D. Wu, et al., Appl. Phys. Lett., 65, 1961 (1994).
Methods have been developed to biaxially texture ReBCO to obtain a high Jc. High Jc""s have been reported in polycrystalline ReBCO in thin films deposited in special substrates on which a biaxially textured non-superconducting oxide buffer layer is first deposited using ion-beam assisted deposition (IBAD) techniques. High Jc""s have also been reported in polycrystalline ReBCO melt-processed bulk material which contains primarily small angle grain boundaries.
Recent developments in biaxially textured metallic substrates such as Rolling Assisted Biaxially Textured Substrates (RABiTS), such as described in U.S. Pat. No. 5,739,086, which is fully incorporated by reference herein, and IBAD on Hastelloy have enabled the fabrication of high Jc high temperature superconductors (HTS) including YBa2Cu3Ox and (Ti, Bi)-1223.
Specifically, in the area of high-temperature superconductor (HTS) wires for power applications, the superconducting materials must be biaxially oriented to assure large critical current densities. These requirements can be satisfied by deposition of HTS films on biaxially oriented substrates. An attractive candidate substrate is thermo-mechanically biaxially textured Ni, which is inexpensive, possesses good mechanical properties, has a high melting temperature (1455xc2x0 C.), and a relatively good oxidation resistance. Unfortunately, direct epitaxy of HTS materials on Ni substrates is exacerbated by chemical reaction and oxidation of the Ni at high temperatures, and by the large crystalline lattice mismatch with all HTS materials. The present invention solves these problems, providing biaxially oriented buffer layers that are chemically and structurally compatible with the subsequent HTS materials.
In general, biaxially-oriented oxide films are epitaxially grown at high temperature and in an oxygen atmosphere. Such deposition conditions may cause oxidation of a non-oxide substrate surface. These effects degrade texturing of films deposited on metallic substrates. X. D. Wu et al have successfully deposited yttria-stabilized-zirconia (YSZ) buffer layers on polycrystalline Ni substrates at room temperature by using ion beam assisted deposition (IBAD), which can solve the oxidation problem. X. D. Wu et al., xe2x80x9cHigh Current YBa2Cu3O7xe2x88x92xcex4 Thick Films On Flexible Ni Substrates With Textured Buffer Layersxe2x80x9d, Appl. Phys. Lett. 65 (15), Oct. 10, 1994, p 1961. However, IBAD is a complex process, which limits its practical applications. In addition, there is no epitaxial relationship between the Ni substrate and the film.
Buffer layers play an important role in superconducting devices, such as a high Tc superconducting laminate tape which consists of high Tc superconducting film, buffer layers, and textured metal substrate. The buffer layers are used not only to transfer the biaxially oriented structure from the substrate to the top high Tc superconducting film, but also to protect the high Tc superconducting film from contamination from the underlying substrate. Insulating buffer layers such as CeO2 and SrTiO3 crack during high temperature annealing, reducing the efficiency of the HTS material. Moreover, insulating buffer layer such as CeO2, SrTiO3, and YSZ, cannot electrically stabilize the HTS conductor layer during transient loss of superconductivity.
Transient loss of superconductivity may cause the superconducting device to overheat. Unstable transient loss of superconductivity may cause portions of the superconducting material to vaporize. An electrically conducting oxide buffer layer would solve the above problems. However, successful deposition of an electrical conductive oxide buffer layer on a biaxially textured polycrystalline metallic substrate has not been disclosed heretofore.
One particular conducting material, LaNiO3, is reported by Kumar et al., xe2x80x9cLaNiO3: A Promising Material for Contact with YBa2CU3O7xe2x88x92x  Thin Filmsxe2x80x9d IEEE Transactions on Applied Superconductivity, Vol. 5, No. 4, December 1995, p. 3498, to have been successfully deposited on YBCO for use as an electrical contact material. This use of LaNiO3 as an electrical contact material is a significantly different use than described herein because the deposition of YBCO on the buffer layer must occur under conditions where the YBCO will form (high temperature and oxygen partial pressure). For electrical contacts, the LaNiO3 can be deposited at lower temperatures on YBCO that has already been formed.
Epitaxial deposition of LaNiO3 and deposition of oxides on LaNiO3 has been disclosed in H. Ichinose et al., xe2x80x9cSynthesis of PbTiO3 film on LaNiO3-coated substrate by the spray-ICP techniquexe2x80x9d J. Materials Science 29 (1994) p5115-5120; Aidong Li et al., xe2x80x9cPreparation of Epitaxial Metallic LaNiO3 Films on SrTiO3 by Metallorganic Decomposition for the Oriented Growth of PbTiO3xe2x80x9d Appl. Phys. Lett. 69 (2), Jul. 8, 1996; and K. M. Satyalakshrni et al., xe2x80x9cEpitaxial Metallic LaNiO3 Thin Films Grown by Pulsed Laser Depositionxe2x80x9d, Appl. Phys. Lett. 62 (11), March 15, 1993, p1233. However, in all of these applications, the epitaxial films are deposited on insulating single crystals.
For further background information, refer to the following publications:
1. K. Sato, et al., xe2x80x9cHigh-Jc Silver-Sheathed Bi-Based Superconducting Wiresxe2x80x9d, JEFE Transactions on Magnetics, 27 (1991) 1231.
2. K. Heine, et al., xe2x80x9cHigh-Field Critical Current Densities in Bl2Sr2Ca1Cu2O8+x/Ag Wiresxe2x80x9d, Applied Physics Letters, 55 (1991) 2441.
3. R. Flukiger, et al., xe2x80x9cHigh Critical Current Densities in Bi(2223)/Ag Tapesxe2x80x9d, Superconductor Science and Technology, 5 (1992) S61.
4. D. Dijkkamp, et al., xe2x80x9cPreparation of Yxe2x80x94Baxe2x80x94Cu Oxide Superconducting Thin Films Using Pulsed Laser Evaporation from High Te Bulk Materialxe2x80x9d, Applied Physics Letters, 51, 619 (1987).
5. S. Mahajan, et al., xe2x80x9cEffects of Target and Template Layer on the Properties of Highly Crystalline Superconducting a-Axis Films of YBa2xe2x80x94Cu3xe2x80x94O7 by DC-Sputteringxe2x80x9d, Physica C., 213, 445 (1993).
6. A. Inam, et al., xe2x80x9cA-axis Oriented Epitaxial YBa2xe2x80x94Cu3xe2x80x94O7xe2x80x94PrBa2Cu3O7 Heterostructuresxe2x80x9d, Applied Physics Letters, 57, 2484 (1990).
7. R. E. Russo, et al., xe2x80x9cMetal Buffer Layers and Yxe2x80x94Baxe2x80x94Cuxe2x80x94O Thin Films on Pt and Stainless Steel Using Pulsed Laser Depositionxe2x80x9d, Journal of Applied Physics, 68, 1354 (1990).
8. E. Narumi, et al., xe2x80x9cSuperconducting YBa2Cu3O Films on Metallic Substrates Using In Situ Laser Depositionxe2x80x9d, Applied Physics Letters, 56, 2684 (1990).
9. J. D. Budai, et al. xe2x80x9cIn-Plane Epitaxial Alignment of YBa2xe2x80x94Cu3xe2x80x94O7 Films Grown on Silver Crystals and Buffer Layersxe2x80x9d, Applied Physics Letters, 62, 1836 (1993).
10. T. J. Doi, et al., xe2x80x9cA New Type of Superconducting Wire; Biaxially Oriented Tl1(Ba0.8Sr0.2)2Ca2Cu3O7 on [100] less than 100 greater than  Textured Silver Tapexe2x80x9d, Proceedings of 7th International Symposium on Superconductivity, Fukuoka, Japan, Nov. 8-11, 1994.
11. D. Forbes, Executive Editor xe2x80x9cHitachi Reports 1-meter Tl-1223 Tape Made by Spray Pyrolysisxe2x80x9d, Superconductor Week, Vol. 9, No. 8, Mar. 6, 1995.
12. Recrystallization Grain Growth and Textures, Papers presented at a seminar of the American Society for Metals, Oct. 16 and 17, 1965, American Society for Metals, Metals Park, Ohio.
13. A. Goyal et al., xe2x80x9cHigh Critical Current Density Superconducting Tapes by Epitaxial of YBa2Cu3Ox Thick Films on Biaxially Textured Metal Substratesxe2x80x9d, Appl. Phys. Lett., 69, 1795 (1996).
14. D. P. Norton et al., xe2x80x9cEpitaxial YBa2Cu3Ox on Biaxially Textured Biaxially Textured (001) Ni: An Approach to High Critical Current Density Superconducting Tapexe2x80x9d, Science, 274, 755 (1996).
15. M. Paranthaman et al., xe2x80x9cGrowth of Biaxially Textured Buffered Layers on Rolled Ni Substrates by Electron Beam Evaporationxe2x80x9d Physica C., 275, 266 (1997).
16. K. M. Satyalakshrni, R. M. Mallya, K. V. Ramanathan, X. D. Wu, B. Brainard, D. C. Gautier, N. Y. Vasanthacharya and M. S. Hegde: xe2x80x9cEpitaxial Metallic LaNiO3 Thin Films Grown by Pulsed Laser Depositionxe2x80x9d Appl. Phys. Lett. 62 (11), Mar. 15, 1993, p1233.
17. Ching-Chyuan Yang, Ming-Sen Chen, Tian-Jue Hong, Chii-Ming Wu, Jenn-Ming Wu, and Tai-Bor Wu, xe2x80x9cPreparation of (100)-oriented Metallic LaNiO3 Thin Films on Si Substrates by Radio Frequency Magnetron Sputtering for the Growth of Textured Pb(Zr0.53Ti0.47)O3xe2x80x9d, Appl. Phys. Lett. 66 (20), May 15, 1995, p2643.
18. Dhananjay Kumar, K. M. Satyalakshmi, M. S. Hegde, Prakash R. Apte, and Richard Rinto, xe2x80x9cLaNiO3: A Promising Material for Contact with YBa2CU3O7xe2x88x92x Thin Filmsxe2x80x9d, IEEE Transactions on Applied Superconductivity, Vol. 5, No. 4, December 1995, p. 3498.
19. H. Ichinose, M. Nagano, H. Katsuki, and H. Takagi, xe2x80x9cSynthesis of PbTiO3 Film on LaNiO3-coated Substrate by the Spray-ICP Techniquexe2x80x9d, J. Materials Science 29 (1994) p5115-5120.
20. Aidong Li, Chuanzhen Ge, and Peng Lu, xe2x80x9cPreparation of Epitaxial Metallic LaNiO3 Films on SrTiO3 by Metallorganic Decomposition for the Oriented Growth Of PbTiO3xe2x80x9d, Appl. Phys. Lett. 69 (2), Jul. 8, 1996.
21. X. D. Wu, S. R. Foltyn, P. Arendt, J. Townsend, C. Adams, I. H. Campbell, P. Tiwari, Y. Coulter, and D. E. Peterson, xe2x80x9cHigh Current YBa2Cu3O7xe2x88x92xcex4 Thick Films on Flexible Ni Substrates with Textured Buffer Layersxe2x80x9d, Appl. Phys. Lett. 65 (15), Oct. 10, 1994, p 1961.
The present invention provides a biaxially textured laminate article having a polycrystalline biaxially textured conductive substrate with an electrically conductive oxide layer epitaxially deposited thereon. Thus, a general objective of providing a laminated article having an electrically conductive buffer layer epitaxially deposited on a polycrystalline biaxially textured substrate is accomplished.
Another objective of the present invention is to provide a biaxially textured laminate article useful for superconductors having a buffer layer which stabilizes a transitioning superconductor layer deposited thereon. This objective is accomplished by providing an electrically conductive oxide buffer layer having a biaxial texture on which a superconducting material can be epitaxially deposited thereon.
Another objective of the present invention is to provide a method of epitaxially depositing an electrically conductive oxide buffer layer onto a metallic substrate. This objective is accomplished by depositing an epitaxial layer of a first electrically conductive oxide film on a biaxially textured metallic substrate in the presence of a first sputtering gas; substituting the first sputtering gas with a second sputtering gas; and depositing an epitaxial layer of a second electrically conductive oxide film on a surface of the first electrically conductive oxide film in the presence of said second sputtering gas.
Still another objective of the present invention is to provide a method of epitaxially depositing an electrically conductive oxide buffer layer onto a metallic substrate without forming metal oxide contaminants on the metal substrate. This objective is accomplished by epitaxially depositing an initial layer of an electrically conductive oxide onto the biaxially textured metallic substrate in the presence of a sputtering gas which is inert or a forming gas.
Further objects of the invention will become apparent from the description and figures provided herein.